1. Field of the Invention
The invention relates to a sensor, a device and a method for measuring blood pressure. This sensor, which is to be applied Lo a part of a live human or, possibly, animal body containing an artery, and the respective device and method are designed to permit non-invasive, long-term measurement of blood pressure in a continuous or at least, quasi-continuous manner, lasting for several hours or days, for instance.
2. The Prior Art
Blood pressure is often measured with instruments that are based on the method of Riva-Rocci and have a hollow, deformable cuff. This is wrapped around a patient's upper arm or some other part of the body, inflated with air and then deflated. As the air is being released, the systolic and the diastolic blood pressure are recorded, based on the Korotkoff sounds generated when the blood flows through an artery, or on some oscillometric measuring method. The Riva-Rocci method is not suitable for any long-term, quasi-continuous kind of measurement, as alternating inflations and deflations of the cuff would be uncomfortable and would probably even damage the patient's health.
Other devices for measuring blood pressure are known, using sensors, for instance, to measure the rate of the blood flow or deformations in the walls of the arteries by means of light or ultrasound. In this context EP-A-0 467 853 is of relevance. Such sensors are comparatively expensive, however, and require most precise positioning.
In U.S. Pat. No. 5,111,826 an instrument for the measurement of blood pressure is described which is provided with a sensor with a piezoelectric force pick-up. For measurement purposes this sensor may be strapped to the patient's finger by means of a fastening device, i.e., a hollow cuff, which is firmly pressed against the finger. The disadvantage of such a sensor is that forces acting upon the force pick-up from outside or as a result of movements of the patient, are likely to produce errors in measurement. Moreover, piezoelectric transducers usually have pyroelectric properties as well, making the sensor sensitive to temperature changes. The cuff, which contains a fluid and subjects the finger to pressure along its entire circumference, may interfere with the patient's blood circulation during long-term measurements, in addition to handicapping him in the use of his hand. Finally, the finger has no large artery that would lend itself to precise measurement.